This invention relates to a recirculating furnace-dryer combination, and more particularly to such a combination in which a greater than atmospheric pressure is maintained throughout the system during operation with dryer gases being recirculated into the combustion chamber of the furnace for incineration to reduce pollution and to produce more efficient operation of the system.
The discharge of air pollutants from furnaces, dryers, etc. is coming under ever increasing control as to the quantities of pollutants which may be allowed to escape into the atmosphere. For this reason, many have attempted to reduce the amounts of pollutants which are allowed to escape into the atmosphere from such operations.
Most furnaces, dryers, etc. now in use have been criticized as failing to provide the complete and efficient combustion necessary to meet air pollution requirements, while others, although possibly meeting the performance requirements are prohibitively expensive. A primary example of the need for increased efficiency and control of air pollution and greater efficiency in combustion is found in veneer, or lumber, dryers. In such dryers, as the veneer, or lumber, is dried, moisture is given off and in this moisture are found hydrocarbons and wood fiber particles.
In the past, it has been a general policy to allow the material released from the wood in the dryer and the exhaust from the furnace merely to escape into the atmosphere producing a highly visible form of pollution. Further, by allowing such materials to merely exhaust to the atmosphere, not only have pollutants been allowed to escape, but considerable quantities of heat energy are lost which is a considerable loss of resources in this period of needed energy conservation.
To further alleviate the energy problem with which we are faced, several have attempted to provide furnaces which are capable of burning waste wood products which are produced in the manufacture of the veneer, or lumber, which is to be dried in the dryer. Although such material may burn, it generally has a high moisture content and thus it has been difficult to burn efficiently and with minimal pollution.
A general object of the present invention, therefore, is to provide a novel furnace-dryer combination including a combustion chamber which produces heated gases which may be routed to dryer, with the gases including pollutants produced in the dryer being recirculated through a substantially closed loop system back into the combustion chamber for reincineration of pollutants and production of relatively clean exhaust from the system.
More specifically, an object of the invention is to provide such a novel combination in which a housing encloses the combustion chamber to maintain an above atmospheric pressure in the combustion chamber, the dryer is constructed to be capable of maintaining a greater than atmospheric pressure therein, and means is provided for returning gases from the dryer under pressure to the housing and thereafter admitting such gases and included pollutant materials from the housing into the combustion chamber at various zones in the combustion chamber to produce efficient and complete combustion of materials within the return gases.
A further object of the invention is to provide such novel combination wherein not only are the return gases with their pollutants reincinerated by introduction into the combustion chamber, but they also are capable of contributing to the heat value of the gases produced in the combustion chamber.
Yet another object is to provide such novel apparatus in which automatic controls are provided for introducing heated gases as required into the dryer to maintain temperatures in the dryer in a preselected range, and means for sensing operational characteristics in the combustion chamberr for feeding fuel and return gases to the combustion chamber as required to maintain a balanced flow of gases through the system to maintain desired temperatures in the dryer.
A still further object is to provide novel a furnace-dryer combination in which solid fuel is fed to the combustion chamber, and an air lock is provided in the fuel feed apparatus to aid in maintaining a pressurized condition within the combustion chamber.
Yet another object of the invention is to provide a novel furnace-dryer combination in which moisture from the solid fuel itself and moisture contained in the return gases from the dryer combine in the combustion chamber to produce moist heated gases for introduction into the dryer to produce faster and more efficient drying of the materials within the dryer.
Another object of the invention is to provide a novel recirculating furnace-dryer combination in which a fan for producing greater than atmospheric pressure within the combustion chamber and dryer is connected in the return conduit through which return gases are recirculated from the dryer to a housing enclosing the combustion chamber, whereby the fan is in a position to pump gases which are coolest in the system, as opposed to being placed in the conduit feeding gases at maximum temperature from the combustion chamber to the dryer. By placing the fan at a position in which the gases supplied thereto are at a minimum temperature there is less injurious effect to the mechanical workings of the fan.
Yet another object of the present invention is to provide a novel recirculating furnace-dryer combination in which selected pressure and temperatures may be maintained throughout the system by a series of automatic control devices without the need for previously used refractory dampers mounted for controlled shifting within the stream of combustion gases in the combustion chamber.
Yet another object of the invention is to provide a novel recirculating furnace-dryer combination which is substantially fully pressurized throughout at a pressure greater than atmospheric pressure, which permits the system to operate at higher enthalpy levels, and produce greater operating efficiencies throughout.
A still further object of the invention is to provide a novel furnace-dryer combination in which the combustion chamber includes a cylindrical vessel into which fuel is placed for burning and the sides of the vessel having openings extending therethrough at angles to lines extending radially from the center of the vessel, whereby gases may be injected through the openings, or nozzles, to produce a swirling, or vortex, movement of materials and gases within the vessel for more complete and efficient combustion.
A still further object is the provision of means for holding a portion of moist fuel in a region adjacent the combustion vessel for drying prior to injecting the materials into the combustion vessel.
These and other objects and advantages will become more fully apparent as the following description is read in conjunction with the drawings.